Various electro-optical systems have been developed for reading optical indicia, such as barcodes. A barcode is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths. In a barcode, the bars and spaces having differing light reflecting characteristics. Some of the barcodes have a one-dimensional structure in which bars and spaces are spaced apart in one direction to form a row of patterns. Examples of one-dimensional barcodes include Uniform Product Code (UPC), which is typically used in retail store sales. Some of the barcodes have a two-dimensional structure in which multiple rows of bar and space patterns are vertically stacked to form a single barcode. Examples of two-dimensional barcodes include Code 49 and PDF417.
Systems that use one or more imaging sensors for reading and decoding barcodes are typically referred to as imaging-based barcode readers, imaging scanners, or imaging readers. A imaging sensor generally includes a plurality of photosensitive elements or pixels aligned in one or more arrays. Examples of imaging sensors include charged coupled devices (CCD) or complementary metal oxide semiconductor (CMOS) imaging chips.
FIG. 1A and FIG. 1B depict an imaging slot scanner 50 in accordance with some embodiments. The imaging slot scanner 50 has a window 56 and a housing 58. The imaging slot scanner 50 is typically a portable reader that has a base for supporting itself on a flat surface 30, such as, a countertop. The window 56 generally faces an operator at the workstation. As shown in FIG. 1A, the operator can slide or swipe the product 40 past the window 56 from right to left, or from left to right, in a “swipe” mode, to let an image of the barcode 40 on the product 42 be captured by the imaging slot scanner 50. Alternatively, the operator can present the barcode 40 on the product 42 to the center of the window 56 in a “presentation” mode. The choice depends on operator preference or on the layout of the workstation. In an imaging slot scanner it is necessary to illuminate the FOV of the imaging camera at a substantial angle to be able to position the illumination system as high as possible to the top of the scanner. It allows hiding the illumination system and minimizing the user exposure to the bright illumination. However it creates challenge to redirect efficiently the light towards the camera imaging FOV. It is generally desirable to reduce light variation from the top to the bottom at the near field close to the window and to increase the range of working distances within which the barcode 40 can be successfully decoded.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.